Blood cortisol: when testing is performed, preparation and interpretation

Cortisol is an adrenal cortex hormone involved in regulating blood sugar, blood pressure, inflammation and the body’s response to stress. Measuring blood cortisol helps a doctor assess whether too much or too little is being secreted, and the result is interpreted alongside the time of day the blood was taken. At Poliklinika Analiza, cortisol is measured in serum.

Who the test is for

• people with signs of excess cortisol (Cushing’s syndrome), such as weight gain mainly around the trunk and face, wide purple stretch marks, easy bruising, weakness of the thigh and upper arm muscles, and raised blood pressure and sugar,
• people with signs of cortisol deficiency (adrenal insufficiency, for example Addison’s disease), such as prolonged fatigue and weakness, loss of appetite and weight, nausea, low blood pressure and dizziness on standing,
• people after prolonged corticosteroid treatment, when a doctor is assessing recovery of their own cortisol secretion,
• people with prolonged fatigue, as part of the Burnout panel, alongside tests for common physical causes of fatigue.

Panels including this test

Test Cortisol is also included in this panel.

Excess hair growth paneltotal and free testosterone, DHEAS, androstenedione, cortisol, FSH and 4164.00€Details ›

All panels including Cortisol (4) ›

What blood cortisol shows

Cortisol secretion is stimulated by the pituitary hormone ACTH (adrenocorticotropic hormone), while sufficient cortisol feeds back to inhibit ACTH secretion. A cortisol result therefore reflects both adrenal and pituitary function.

Cortisol is not a measure of a “stress level”, and one result does not confirm burnout. With prolonged fatigue, checking common physical causes such as anaemia, thyroid disorders or vitamin deficiency is more useful. We discuss the syndrome itself in the article Burnout syndrome.

Daily rhythm and blood collection timing

Cortisol rises in the early morning, peaks between 7 and 9, then falls to its lowest level around midnight. The same value may therefore be normal at 8 in the morning but too high at 17.

Depending on the doctor’s recommendation, blood is taken in the morning, afternoon or at both times. Tell staff if you work night shifts because the rhythm is then shifted.

Medicines that affect results

Corticosteroids in tablets, injections, inhalers, nasal sprays and creams suppress the body’s own cortisol production with prolonged use, so the result can be low. Hydrocortisone is cortisol itself, while the test partly measures prednisolone, methylprednisolone and, to a lesser extent, prednisone as cortisol, so the result can be higher than the body’s own secretion. Do not stop treatment yourself because sudden withdrawal can be dangerous; a doctor decides whether to pause it.

Oral contraception and other oestrogen preparations increase cortisol-binding globulin (CBG) in the blood, so total serum cortisol is higher even though free, active cortisol does not change to the same extent. When investigating raised cortisol, guidelines advise stopping oestrogen preparations six weeks before testing if possible, in agreement with a doctor.

Preparing for blood collection

• Come rested and avoid strenuous training the day before (more in the article on stress hormones).
• Bring a list of medicines, including creams, inhalers and contraception. If you take corticosteroids in the morning, agree with your doctor whether to take the dose before or after blood collection.
• If you take biotin (for example hair and nail supplements), mention it during blood collection.

Cortisol in blood, saliva and urine

Serum shows total cortisol at the time of collection, and morning serum cortisol is the first step when deficiency is suspected. Saliva and 24-hour urine show free cortisol: saliva late at night, when it should be lowest, and urine over the whole day. For Cushing’s syndrome, Endocrine Society guidelines list these or the dexamethasone suppression test as initial tests, rather than a randomly measured serum cortisol, and require two different tests with matching findings. In that test, blood cortisol is measured in the morning after a dexamethasone tablet the previous evening. At Poliklinika Analiza, cortisol is measured in serum, while a doctor can request saliva and urine tests.

How to interpret a cortisol result

The result is read alongside collection time. Reference intervals for morning and afternoon samples depend on the method, so those printed on your report apply, rather than figures from the internet or older reports.

• Raised cortisol often does not originate from the adrenal or pituitary gland: it rises with stress and acute illness, with oestrogen and in pregnancy, and is also higher in depression, alcoholism, marked obesity and anorexia nervosa. One raised result does not establish Cushing’s syndrome.
• Low morning cortisol may indicate adrenal or pituitary insufficiency, but also secretion suppressed by corticosteroids. A doctor usually also requests ACTH, and an ACTH stimulation test for confirmation.

A doctor, most often a GP or endocrinologist, interprets the result alongside symptoms, medicines and examination.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). You can also use the same page to ask about panels containing cortisol. Prices for all tests and panels are in the price list.

Frequently asked questions

Do I need to fast for cortisol?

Fasting is not essential for cortisol alone. If glucose, lipids or the Burnout panel are being measured alongside it, come fasting.

Can cortisol be measured with a home test or at a pharmacy?

Saliva for cortisol can be collected at home in a special tube at a precisely specified time, but is analysed in a laboratory. It makes sense when requested by a doctor, most often for suspected Cushing’s syndrome; a sample taken without a clear reason is difficult to interpret.

Does “adrenal fatigue” exist?

Not as a recognised diagnosis. A systematic review of research from 2016 (BMC Endocrine Disorders) found no evidence that such a condition exists. Exhaustion is a real problem, but its cause should be investigated with a doctor, from sleep and blood count to thyroid function and mood.